Equipment for sealing a cardboard based container containing, for instance, a heat sensitive food product powder is known from e.g. EP0074343. Such equipment normally includes a welding unit where a lid is applied to the container in a gas-tight manner by inducing welding energy and melting a weldable, plastic layer that forms part of the container and/or the lid. Such a welded joint is well known to be capable of being gas tight.
Often both the container and the lid form multilayer structures where cardboard forms a supporting layer and where a weldable layer made of a plastic film is applied to the inside of the lid and container. In particular for food products, the layer structure usually includes an aluminium foil arranged between the cardboard and the plastic layer. Typically, a high frequency current energy is induced in the aluminium layer, which foil thereby gets heated and in turn melts the plastic film. Automated equipment of this type further comprises transporting means configured to transport a flow of containers to and from the welding unit.
Equipment for manufacturing of the container, for filling the containers and for applying an additional, outer lid is usually arranged in connection to the sealing equipment.
An important issue in this context is the production rate, i.e. the number of containers per, say, minute that can be supplied with a lid. To be commercially successful, the apparatus used for applying the lids must allow for a high production rate.
A problem when trying to increase the production rate of conventional equipment is that the weldable layer does not get sufficient time to heat up, cool and harden before the containers are removed and transported away from the welding unit. This often results in a damaged and leaking joint. Various heating and cooling devices, as well as different weldable material, have been proposed for carrying out the welding step more quickly but their performance has not been satisfactory.
Thus. there is still a need for equipment of the above mentioned type that allow for a higher production rate.